Hundreds of unassigned child protection and adult sexual assault cases, and challenges fighting fraud and cybercrime, are among the reasons revealed for the big expansion in police numbers.

In late August, police were investigating less than 5 per cent of fraud cases referred from the banking sector.

And a huge surge in mental health and family violence incidents meant police workloads were often outstripping population growth.

The practical and political challenges that sparked this year’s decision to hire more than 1000 new staff are outlined in Cabinet documents released after inquiries by Stuff under the Official Information Act.

National campaigned on having one cop for every 500 people, but wasn’t getting any closer to achieving that.

For existing police, challenges were growing on multiple fronts. Mental health callouts almost doubled in a decade, to one every 13 minutes.

Late last year, there were 446 unassigned child protection and adult sexual assault cases, a number that had not improved for two years.

And family violence incidents increased 55 per cent in just seven years.

Children’s Commissioner Judge Andrew Becroft, said children were “just about always” caught up in family violence.

He said the professionalism and “utter concern” of police assigned to child abuse cases impressed him.

But it was equally clear police had struggled with a “growing burden” in this area. Becroft said he was pleased to hear resourcing issues were being taken seriously.

The surge in reports could reflect society’s decreasing toleration of domestic abuse, he said.

Reflecting on the extremely low rates of fraud investigation, Collins said fraud and money-laundering were predicted to pose “an increasing challenge”.

Customers were often the victims in such fraud cases, New Zealand Bankers’ Association chief executive Karen Scott-Howman said.

She was aware of the low investigation rate. “It is a concern for us. My understanding is it’s a reflection of the police’s resourcing.”

Police Association president Chris Cahill said fraud had been a low priority for police over the past 10-15 years, simply because of work needed in other areas, such as child sexual abuse and burglary.

But he did not agree that should continue to be the case. “A number of fraud victims suffer a significant loss, and often their cases are not being picked up, so extra numbers there would really help.

“The Serious Fraud Office pick up about 40 cases a year, which is a relatively small number to what’s being reported.”

A $503 million package, increasing police staff by 1125, was announced on February 2. It came with multiple recommendations covering new staff, and where to assign them.

One proposal was to have up to 40 of 140 extra officers for regional and rural areas forming a Rural Duties Officer Network.

In other developments, police planned to expand the number of tactical crime units, with new units targeting burglary, robbery, theft, scams and violence.

The Cabinet papers suggested police had already made all the savings and productivity gains they possibly could through improved technology.

An estimated 520,000 hours of productivity savings were all eaten up “responding to increasing demand”, Collins wrote.

Broader discussion about the drivers of crime was also a feature of decision-making, with new Police Minister Paula Bennett writing that the police force “cannot arrest its way to lower crime and safer communities”.

Rather, police would need to make use of non-court resolutions for youth offenders and low-level crimes, and better intelligence to target and reduce crime and other anti-social behaviour.

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